Endoscopic treatment instrument

ABSTRACT

An endoscopic treatment instrument is provided comprising: a cylinder adapted to be fitted over a tip of an insertion section of an endoscope; a loop-shaped snare wire which protrudes in the cylinder from a snare sheath that is extendable and retractable with respect to the insertion section and which is extendable within the cylinder; a hooked portion which is formed and radially inwardly extended from the circumference of the tip of cylinder and which holds the snare wire within the cylinder; a locking portion which is provided on the hooked portion and retains a folded-back portion of the snare wire that is forwardly moved toward the cylinder tip with respect to the snare sheath and by means of which the snare wire is turned upside-down around the folded-back portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an endoscopic treatment instrument.Priority is claimed on Japanese Patent Application No. 2006-257351,filed Sep. 22, 2006, the content of which is incorporated herein byreference.

2. Description of the Related Art

With respect to early-stage cancer of the stomach or esophagus, anendoscopic demucosation is performed in which a mucosa in an ailing oraffected area is excised by using a frequency snare introduced into abody cavity through a channel of the endoscope. In such a demucosationaloperation, an endoscopic treatment instrument is used which includes agenerally cylindrical transparent cap that is fitted over the tip of aninsertion section of the endoscope.

In an operation with the use of this endoscopic treatment instrument, asnare wire of the high frequency snare is firstly extended radially inthe transparent cap and then a mucosa to be excised is absorbed so as toform the shape of a polyp in the transparent cap while the snare wire isextended as it is. Thereafter, a base portion of the polyp-shaped mucosais excised by the use of the frequency snare. At this time, it isnecessary for the snare wire to be precisely placed on the base portionof the polyp-shaped mucosa drawn in the transparent cap. To this end,there is a proposal in which a hooked portion is provided on the tip ofthe transparent cap and the snare wire is extended along the hookedportion and retained as it is. See, e.g., Japanese Unexamined PatentApplication, First Publication Nos. 2002-45369 and 2004-230054.

With the above-described conventional endoscopic treatment instrument,it is impossible to extend the snare wire in the transparent cap whilemaintaining the transparent cap in a floating state or so as to beuntouched. Namely, when the snare wire is extended, the transparent capis inevitably pressed against tissues or mucosa. As such, thetransparent cap is firstly pressed against a normal area or tissue andthe snare wire is then projected through a treatment tool insertionchannel. At this time, the affected area necessarily goes out of view ofthe endoscope. So, it takes a lot of time and trouble to find theaffected area again for excising the polyp thereof. Furthermore, a lotof skill is necessary to speed up a pre-looping operation in which thesnare wire is extended (or a loop of the snare wire is widened) in thetransparent cap. Furthermore, since the snare wire is forwardly andrearwardly moved through the treatment tool insertion channel of theinsertion section, it is necessary to pull out the treatment toolconcerned in order to replace it with another treatment tool such as aninjection needle and the like.

SUMMARY OF THE INVENTION

In light of the circumstances, the present invention has been made andhas an aim of providing a endoscopic treatment instrument in which, evenwhen the cylinder or cap is floating or cantilevered, it is possible toextend (or widen the loop of) the snare wire in the cylinder.

In order to attain the above object, the present invention employs thefollowing means. According to the present invention, an endoscopictreatment instrument is provided comprising: a cylinder adapted to befitted over a tip of an insertion section of an endoscope; a loop-shapedsnare wire which protrudes in the cylinder from a snare sheath that isextendable and retractable with respect to the insertion section andwhich is extendable within the cylinder; a hooked portion which isformed and radially inwardly extended from the circumference of the tipof cylinder and which holds the snare wire within the cylinder; alocking portion which is provided on the hooked portion and retains afolded-back portion of the snare wire that is forwardly moved toward thecylinder tip with respect to the snare sheath and by means of which thesnare wire is turned upside-down around the folded-back portion.

According to the present invention, due to the existence of the lockingportion, it is possible to make the folded-back portion of the snarewire protruding through the snare sheath abut against the hooked portion3 such that the folded-back portion is locked or hooked. At this time,by forwardly moving the snare wire with respect to the snare sheath tothereby generate compression force in the snare wire, it is possible todevelop the loop of the snare wire along the hooked portion with thefolded-back portion functioning as a base point.

Preferably, the locking portion is disposed at a front side in aprotruding direction of the snare wire with respect to the snare sheath.

According to the present invention, by simply making the snare wireprotrude through the snare sheath, it is possible for the folded-backportion of the snare wire to abut against the locking portion.

Preferably, the locking portion includes an auxiliary hooked portionwhich protrudes from an end portion, in the vicinity of which theextension of the snare wire intersects, of the hooked portion toward abase end side of the cylinder.

According to the present invention, it is possible to make thefolded-back portion of the snare wire abut against the hooked portionand to block the forward movement of the folded-back portion of thesnare wire by the auxiliary hooked portion.

Preferably, the locking portion includes a depressed portion orthrough-hole which is provided on the hooked portion in the vicinity ofwhich the extension of the snare wire intersects.

According to the present invention, it is possible to appropriately hookthe folded-back portion at the depressed portion or the through-hole andturn the snare wire upside-down with respect to the hooked portion.

Preferably, the locking portion includes a friction generating portionwhich is provided on an outer surface of the hooked portion and whichhas a larger coefficient of friction than the outer surface of thehooked portion.

According to the present invention, it is possible to hook thefolded-back portion due to high friction force generated by the frictiongenerating portion and to extend the snare wire with the folded-backportion as it is.

Preferably, the endoscopic treatment instrument further comprises a tubewhich opens at its tip in the cylinder and in which the snare sheath isreceived so as to be extendable and retractable.

According to the present invention, by inserting the snare sheath intothe tube, it is possible to insert a treatment tool other than the snarewire into the treatment tool insertion channel of the insertion sectionof the endoscope. Thus, it is possible to decrease the number oftaking-out and putting-in operations of the frequency snare at the timeof using a plurality of different treatment tools.

According to the present invention, it is possible to extend the snarewire in the cylinder while maintaining the cylinder in a floating stateor so as to be untouched.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general schematic view illustrating an endoscope hoodaccording to a first embodiment of the present invention.

FIG. 2 is a schematic view illustrating an endoscope on which theendoscope hood according to the first embodiment of the presentinvention is mounted.

FIG. 3 is a cross-sectional view illustrating a main portion of theendoscope hood according to the first embodiment of the presentinvention.

FIG. 4 is a frontal view of the endoscope hood according to the firstembodiment of the present invention.

FIG. 5 is a plan view illustrating a high frequency snare that is usedtogether with the endoscope hood according to the first embodiment ofthe present invention.

FIG. 6 is a view illustrating an operational state of the endoscope hoodaccording to the first embodiment of the present invention when viewedfrom the endoscope side.

FIG. 7 is a view illustrating a further operational state of theendoscope hood according to the first embodiment of the presentinvention when viewed from the endoscope side.

FIG. 8 is a view illustrating a yet further operational state of theendoscope hood according to the first embodiment of the presentinvention when viewed from the endoscope side.

FIG. 9 is a view illustrating a still further operational state of theendoscope hood according to the first embodiment of the presentinvention when viewed from the endoscope side.

FIG. 10 is a view illustrating a different operational state of theendoscope hood according to the first embodiment of the presentinvention when viewed from the endoscope side.

FIG. 11 is a cross-sectional view illustrating a main portion of anendoscope hood according to a second embodiment of the presentinvention.

FIG. 12 is a cross-sectional view illustrating a main portion of anendoscope hood according to a third embodiment of the present invention.

FIG. 13 is a partial cross-sectional view illustrating a state in whichan injection needle is inserted through the endoscope hood according tothe third embodiment of the present invention.

FIG. 14 is a partial cross-sectional view illustrating a state in whichthe high frequency snare is inserted in the endoscope hood according tothe third embodiment of the present invention.

FIG. 15 is a cross-sectional view illustrating a main portion of anendoscope hood according to a fourth embodiment of the presentinvention.

FIG. 16 is a cross-sectional view illustrating a main portion of anendoscope hood according to a fifth embodiment of the present invention.

FIG. 17 is a plan view of the endoscope hood according to the fifthembodiment of the present invention.

FIG. 18 is a cross-sectional view illustrating a main portion of anendoscope hood according to a sixth embodiment of the present invention.

FIG. 19 is a plan view of the endoscope hood according to the sixthembodiment of the present invention.

FIG. 20 is a partial cross-sectional view illustrating a modifiedexample of the endoscope hood according to the third embodiment ofpresent invention.

FIG. 21 is a partial cross-sectional view illustrating a modifiedexample of the endoscope hood according to the first embodiment ofpresent invention.

FIG. 22 is a partial cross-sectional view illustrating a furthermodified example of the endoscope hood according to the first embodimentof present invention.

FIG. 23 is a partial cross-sectional view illustrating a yet furthermodified example of the endoscope hood according to the first embodimentof present invention.

FIG. 24 is a partial cross-sectional view illustrating a still furthermodified example of the endoscope hood according to the first embodimentof present invention.

FIG. 25 is a partial cross-sectional view illustrating a differentmodified example of the endoscope hood according to the first embodimentof present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed with reference to the drawings. However, it should not beconstrued that the present invention is limited to these embodiments,but rather, components of these embodiments may be combined ifnecessary.

Referring now to FIGS. 1 to 10, a description will be given of a firstembodiment according to the present invention.

As illustrated in FIGS. 1 to 4, an endoscope hood (endoscopic treatmentinstrument) 1 is provided with a transparent cylindrical cap portion(cylinder) 2 the proximal end of which is fitted on the tip of aninsertion section I1 of an endoscope E1 via a fitting portion 7(described later). As illustrated in FIG. 5, a high frequency snare S isforwardly and rearwardly movable with respect to the insertion sectionI1 and includes a snare sheath SS and a snare wire SW which isprotrudable in a meniscus or looped shape through the snare sheath SS.The endoscope hood 1 is used when the snare wire SW is projected intothe cap portion 2 and then radially extended.

The endoscope hood 1 is provided with a hooked portion 3 which isradially inwardly extended from the circumference of the tip of the capportion 2 and which retains within the inside of the cap portion 2 theloop-shaped snare wire SW in an extended manner, with a locking portion5 which is formed on the hooked portion 3 and which swingably catches afolded-back portion W of the tip of the snare wire SW that is forwardlymoved toward the tip of the cap portion 2 with respect to the snaresheath SS, and with a flexible tube (pipe portion) 6 which has a frontalend opened within the cap portion 2 and in which the snare sheath SS isextendably and retractably received.

At the proximal end side, a protruding portion 2A is provided whichcontrols insertion of the insertion portion I1 of the endoscope E1within the cap portion 2. The cylindrical fitting portion 7 is providedso that the cap portion 2 is detachably secured to the tip of theinsertion portion I1. The fitting portion 7 and the cap portion 2 areconnected with a common center axis C. The flexible tube 6 has a centeraxis C1 which is separately disposed parallel to the center axis C. Thecap portion 2 includes a tip end aperture plane 2 a that is formed andslanted at a predetermined angle with respect to the center axis C ofthe cap portion 2 such that the length from the proximal end of the capportion 2 to an intersecting point between the tip end aperture plane 2a and the center axis C1 of the flexible tube 6 is shorter than anyother corresponding length.

The hooked portion 3 is formed along the tip end aperture plane 2 a andhas a length so as to prevent the snare wire SW from protruding when thesnare wire SW is extended in the cap portion 2.

The locking portion 5 is provided with an auxiliary hooked portion 8that is formed by being bent at an end part, in the vicinity of anintersecting point between the hooked portion 3 and the center axis C1of the flexible tube 6, of the hooked portion 3 and by being extendedtoward the proximal end of the cap portion 2. The auxiliary hookedportion 8 and the hooked portion 3 may be integrally formed in one pieceor may be separately formed and then assembled.

The flexible tube 6 is connected into a communication hole 2B which isformed on the side of the cap portion 2, so that it communicates withthe inside of the cap portion 2. The flexible tube 6 has substantiallythe same length as the insertion section I1 and has a proximal end towhich an attaching section 10 that is suspended by and fixed to aforceps opening V of the endoscope E1 is connected, as illustrated inFIG. 1. The attaching section 10 is provided with a hook hole 10A intowhich the forceps opening V is insertable. The attaching section 10 isalso provided with an air-tight valve (gas-tight valve) 11 into whichthe snare sheath SS is inserted.

A control portion main body H is provided on the proximal end of thesnare sheath SS. A slider SL is connected to the proximal end of thesnare wire SW such that it is advanceable and retractable with respectto the control portion main body H.

Next, with further reference to FIGS. 6 to 10, a description will begiven of the operation of the endoscope hood 1 according to the presentembodiment. Here, the following is a sequence or procedure of cutting anunillustrated mucosa (endoscopic demucosation) by the use of theendoscope E1 with the endoscope hood 1 fitted thereon.

Firstly, the fitting portion 7 of the endoscope hood 1 is fitted overthe tip of the insertion section I1 of the endoscope E1, and then, theflexible tube 6 is fixedly secured along the insertion section I1 by theuse of tape for medical use. The thus-conditioned insertion section I1is inserted in a body cavity, and then, the tip end aperture plane 2 aof the cap portion 2 is positioned in the vicinity of a mucosa portionto be excised while it is being observed.

Subsequently, the snare sheath SS is inserted through the air-tightvalve 11 into the flexible tube 6 until the tip thereof protrudes intothe inside of the cap portion 2. Thereafter, the slider SL is forwardlymoved or advanced with respect to the control portion main body H, sothat the folded-back portion W of the snare wire SW protrudes from thesnare sheath SS, as illustrated in FIG. 3, and then abuts against thehooked portion 3 and hence engages the auxiliary hooked portion 8, asillustrated in FIG. 6.

Then, as illustrated in FIG. 7, when the folded-back portion W is hookedat the auxiliary hooked portion 8 and then the snare wire SW is furtherprojected through the snare sheath SS, the folded-back portion W of thesnare wire SW is retained as it is, and one side of the snare wire SW isonly forwardly moved while swaying rightward and leftward. At this time,as illustrated in FIGS. 8 and 9, the movement of the other side of thesnare wire SW, i.e., the folded-back portion W of the snare wire SW isblocked whereas the one side of the snare wire SW is moved along thehooked portion 3 such that the loop of the snare wire SW is widened inthe cap portion 2. As illustrated in FIG. 10, the loop of the snare wireSW is finally formed extending throughout the circumference of thehooked portion 3.

In this state, an injection needle is extended through a treatment toolinsertion channel (not shown) that is provided on the insertion sectionI1, into the inside of the cap portion 2 and then a physiological salinesolution is injected for the swelling. Thereafter, the suction operationis carried out through the treatment tool insertion channel.Thus-suctioned (or drawn) mucous membrane is received in (the loop of)the snare wire SW that has been extended and then the binding andenergizing operation relating to the snare wire is carried out by theuse of the movement of the slider SL. Note that the swelling operationmay be carried out by the use of the injection needle before theextension of the snare wire SW.

With this endoscope hood 1, due to the existence of the locking portion5, it is possible to make the folded-back portion W of the snare wire SWprotruding through the snare sheath SS abut against the hooked portion 3and to block the forward movement of the folded-back portion of thesnare wire SW in the cap portion 2 by the auxiliary hooked portion 8. Atthis time, by forwardly moving the snare wire SW with respect to thesnare sheath SS to thereby generate compression force in the snare wireSW, it is possible to develop the loop of the snare wire SW along thehooked portion 3 with the folded-back portion W (which has been hookedto the locking portion 5) functioning as a base point. Therefore, it ispossible to extend the snare wire SW in the cap portion 2 even when thecap portion 2 is in a floating state.

Further, by inserting the snare sheath SS into the flexible tube 6, itis possible to insert a treatment tool other than the snare wire SW intothe treatment tool insertion channel of the insertion section I1 of theendoscope E1. Thus, it is possible to decrease the number of removal andinsertion operations of the frequency snare S.

Next, with reference to FIG. 11, a description will be given of a secondembodiment of the present invention.

Note that components which are the same or equivalent as those of theabove-mentioned first embodiment are assigned the same referencenumerals and that duplicate descriptions are appropriately omitted.

The second embodiment is different from the first embodiment in that alocking portion 22 of a cap portion 21 of an endoscope hood 20 accordingto the second embodiment is provided with a depressed portion 25 formedin a hooked portion 23 in the vicinity of a position toward which thesnare wire SW is advanced.

The depressed portion 25 is positioned at a position where the centeraxis C1 of the flexible tube 6 and the hooked portion 23 intersect. Itis formed with a depth such that the folded-back portion W of the snarewire SW is partially insertable therein. Note that the presentembodiment may be settled or completed without the auxiliary hookedportion 8.

Next, a description will be given of an operation of the endoscope hood20 according to the second embodiment of the present invention.

Firstly, similarly to the first embodiment, the insertion portion I1with the cap portion 21 fitted thereover is positioned or placed in thevicinity of a section which is to be cut from a mucosa. Subsequently,the tip of the snare sheath SS is projected in the cap portion 21 andthe folded-back portion W of the snare wire SW is projected through thesnare sheath SS.

On this occasion, a part of the folded-back portion W of the snare wireSW is inserted and hooked in the depressed portion 25. Then, when thesnare wire SW is projected through the snare sheath SS, the folded-backportion W of the snare wire SW is retained or held in the depressedportion 25 whereas one side portion of the snare wire SW only protrudeswhile swaying. In this way, the snare wire SW is extended in the capportion 21 so as to follow the hooked portion 23 whereby a loop of thesnare wire SW is formed extending throughout the circumference of thehooked portion 23.

With this endoscope hood 20, it is possible to obtain an operation andeffects which are similar to those of the first embodiment.Specifically, since the locking portion 22 is provided with depressedportion 25 and since the folded-back portion W of the snare wire SW isengaged in the depressed portion 25, it is possible to appropriatelyhook the folded-back portion at the hooked portion 23 and turn the snarewire upside-down, as compared to a case in which the folded-back portionW is hooked at the auxiliary hooked portion 8.

Next, with reference to FIGS. 12 to 14, a description will be given of athird embodiment of the present invention.

Note that components which are the same or equivalent as those of theabove-mentioned first and second embodiments are assigned the samereference numerals and that duplicate descriptions are appropriatelyomitted.

The third embodiment is different from the second embodiment in that alocking portion 32 of a cap portion 31 of an endoscope hood 30 accordingto the third embodiment is provided with a through-hole 35, in stead ofbeing provided with the depressed portion 25, which is formed in ahooked portion 33 and having a constant inside diameter as shown in FIG.12. Note that the present embodiment may be settled or completed withoutthe auxiliary hooked portion 8.

The through-hole 35 has a dimension such that the injection needle NE isinsertable therethrough as shown in FIG. 13 and that the folded-backportion W of the snare wire SW is not insertable therethrough as shownin FIG. 14. This is intended for treating with the injection needle NEinserted through the flexible tube 6.

With this endoscope hood 30, it is possible to obtain an operation andeffects which are similar to those of the second embodiment.

Next, with reference to FIG. 15, a description will be given of a fourthembodiment of the present invention.

Note that components which are the same or equivalent as those of theabove-mentioned first, second and third embodiments are assigned thesame reference numerals and that duplicate descriptions areappropriately omitted.

The fourth embodiment is different from the first embodiment in that anendoscope hood 40 according to the fourth embodiment is not providedwith the flexible tube 6. Namely, a cap portion 41 is not formed with athrough-hole.

An insertion section I2, over which the cap portion 41 is fitted, of anendoscope E2 is provided with a first treatment tool insertion channelCH1 and a second treatment tool insertion channel CH2 which is disposedcloser to a center axis C2 of the insertion section I2 than the firsttreatment tool insertion channel CH1 is. With this insertion section I2,it is possible to carry out a treatment, for example, by inserting thesnare sheath SS into the first treatment tool insertion channel CH1 andby inserting another treatment tool into the second treatment toolinsertion channel CH2.

A hooked portion 42 is formed such that it intersects with a center axisC3 of the first treatment tool insertion channel CH1, that it does notintersect with a center axis C4 of the second treatment tool insertionchannel CH2, and that it is extended radially inwardly. Therefore, evenwhen the cap portion 41 is fitted over the insertion section I2 of theendoscope E2, it is possible for a treatment tool that is inserted inthe second treatment tool insertion channel CH2 to protrude from a tipend aperture plane 41 a of the cap portion 41 toward the tip side.

Next, a description will be given of an operation of the endoscope hood40 according to the fourth embodiment of the present invention.

Firstly, the fitting portion 7 of the endoscope hood 40 is fitted overthe tip of the insertion section I2 of the endoscope E2, and then, thethus-fitted insertion section I2 is inserted in a body cavity such thatthe tip end aperture plane 41 a of the cap portion 41 is disposed in thevicinity of a mucosa portion to be cut or excised.

Subsequently, the snare sheath SS is inserted into the first treatmenttool insertion channel CH1 such that the tip thereof protrudes withinthe cap portion 41. Then, an unillustrated slider is forwardly movedtoward the tip side with respect to the control portion main body suchthat the folded-back portion W of the snare wire SW is projected fromthe snare sheath SS. At this time, the folded-back portion W abutsagainst the hooked portion 42 and then engages the auxiliary hookedportion 8. Thereafter, the snare wire SW is radially andcircumferentially extended along the hooked portion 42 under a principlesimilar to that of the first embodiment.

While injecting a physiological saline solution by the use of theinjection needle NE, the injection needle NE is projected in the capportion 41 through the second treatment tool insertion channel CH2. Atthis time, the injection needle NE is not hooked at the hooked portion42 and the auxiliary hooked portion 8, but it protrudes through the tipend aperture plane 41 a to thereby puncture a mucous membrane.

In this way, after the swelling operation in which a physiologicalsaline solution is injected has been completed, the suction operation iscarried out by the use of the second treatment tool insertion channelCH2 to raise or protrude the mucous membrane and then the binding andenergizing operation is carried out by the use of the snare wire thathas been extended or by the use of the loop thereof that has beenexpanded or widened.

With this endoscope hood 40 in which the flexible tube 6 is not providedand which is simply fitted over the insertion section I2 of theendoscope E2 with the two channels provided therein, it is possible toobtain an operation and effects which are similar to those of the firstembodiment.

Next, with reference to FIGS. 16 and 17, a description will be given ofa fifth embodiment of the present invention.

Note that components which are the same or equivalent as those of theabove-mentioned first to fourth embodiments are assigned the samereference numerals and that duplicate descriptions are appropriatelyomitted.

The fifth embodiment is different from the first embodiment in that acap portion 51 of an endoscope hood 50 according to the fifth embodimentincludes a tip end aperture plane 51 a that is formed and slanted at apredetermined angle with respect to the center axis C of the cap portion51 such that the length from the proximal end of the cap portion 51 toan intersecting point between the tip end aperture plane 51 a and thecenter axis C1 of the flexible tube 6 is longer than any othercorresponding length.

Since a side surface of the cap portion 51 forms an acute angle with thehooked portion 3 in the vicinity of the intersecting point describedabove, during the extension of the snare wire SW in the cap portion 51,it is possible to more preferably turn the snare wire SW toward theproximal end side of the cap portion 51 and then more appropriatelyextend the snare wire SW along the hooked portion 3, as compared to thefirst embodiment. Therefore, as compared to the endoscope hood 1according to the first embodiment, it is possible to more effectivelyprevent the snare wire SW from departing from the hooked portion 3 oncethe snare wire SW is put in position along the hooked portion 3.

Next, with reference to FIGS. 18 and 19, a description will be given ofa sixth embodiment of the present invention.

Note that components which are the same or equivalent as those of theabove-mentioned first to fifth embodiments are assigned the samereference numerals and that duplicate descriptions are appropriatelyomitted.

The sixth embodiment is different from the first embodiment in that anauxiliary hooked portion 61 of an endoscope hood 60 according to thesixth embodiment is not provided only in the vicinity of a position atwhich the hooked portion 3 and the center axis C1 of the flexible tube 6intersect, but provided all around the circumference of hooked portion 3and formed so as to bend at the internal edge of the hooked portion 3and to extend toward the proximal end side of a cap portion 62

With this endoscope hood 60 in which a gutter or cradle 63 for receivingthe snare wire SW is formed by the hooked portion 3, the auxiliaryhooked portion 61 and an inner surface of the cap portion 62, it ispossible to effectively prevent the snare wire SW from departing fromthe hooked portion 3 once the snare wire SW is extended in the capportion 62 and put in position along the hooked portion 3.

Note that the technical scope of the present invention is not limited tothe embodiments described above and that various modifications can bemade without departing from the scope of the subject matter of thepresent invention.

For example, although the locking portion 32 is provided with thethrough-hole 35 whose internal diameter is constant in the thirdembodiment, as illustrated in FIG. 20, a hooked portion 72 may beprovided with a through-hole 71 whose internal diameter is graduallydecreased in accordance with the approaching the tip side of a capportion 70. With this structure, it is possible to appropriately preventthe snare wire SW from breaking through the through-hole 71.

Further, as illustrated in FIG. 21, an auxiliary hooked portion 73 maybe formed so as to be curved and extended toward the proximal end sideof a cap portion 75 with an inclination toward the center axis C. Withthis structure, when the snare wire is radially extended, it is possibleto firmly catch or hook the snare wire by the auxiliary hooked portion73.

Further, as illustrated in FIG. 22, in a cross-sectional planecontaining the center axis C of a cap portion 76, an auxiliary hookedportion 77, a hooked portion 78 connected to the auxiliary hookedportion 77, and an inner surface of the cap portion 76 may form acontinuous line SU curved with substantially the same center ofcurvature. With this structure, it is possible to firmly catch or hook afolded-back portion of the snare wire.

Further, as illustrated in FIG. 23, a hooked portion 80 may be formedwith a locking portion 82 such that the thickness thereof along thecenter axis C is gradually increased in accordance with the approachingthe center axis. With this structure, it is possible to firmly catch orhook the folded-back portion W of the snare wire SW since thefolded-back portion W is radially outwardly biased when it comes incontact with a locking portion 82.

Further, as illustrated in FIG. 24, a locking portion 83 may be formedon a portion, or throughout the circumference, of a top surface of thehooked portion 3 and provided with a friction generating portion 85which has a larger coefficient of friction than that of the top surfaceof the hooked portion 3. With this structure, it is possible to catch orhook the folded-back portion W such that the snare wire can be turnedupside-down therearound due to high friction force generated when thefolded-back portion W of the snare wire abuts against the frictiongenerating portion 85.

Furthermore, instead of disposing the hook hole 10A into which theforceps opening V is insertable, as illustrated in FIG. 25, anattachment 86 may be provided which has an attaching surface 86A throughwhich it is detachably attachable anywhere to a bending preventionsection B or in the vicinity of a control portion A near the forcepsopening V of the endoscope E1. With this structure, when detached, theattachment 86 is not an obstruction that blocks the operation related tothe forceps opening V.

While preferred embodiments of the invention have been described andillustrated above, it should be understood that these are exemplary ofthe invention and are not to be considered as limiting. Additions,omissions, substitutions, and other modifications can be made withoutdeparting from the scope of the present invention. Accordingly, theinvention is not to be considered as being limited by the foregoingdescription, and is only limited by the scope of the appended claims.

1. An endoscopic treatment instrument comprising: a cylinder adapted to be fitted over a tip of an insertion section of an endoscope; a loop-shaped snare wire which protrudes in the cylinder from a snare sheath that is extendable and retractable with respect to the insertion section and which is extendable within the cylinder; a hooked portion which is radially inwardly extended from the circumference of a tip of the cylinder and which holds the snare wire within the cylinder; a locking portion provided on the hooked portion in front of a distal end of the snare wire and the snare sheath so as to face the distal end of the snare wire and the snare sheath; and an auxiliary hooked portion bent at an end part of the hooked portion and extending toward the proximal end of a cap portion, wherein when the snare wire advances to the locking portion, the locking portion contacts a folded-back portion of the snare wire and the locking portion and the auxiliary hooked portion holds the folded-back portion.
 2. The endoscopic treatment instrument as recited in claim 1, wherein the auxiliary hooked portion protrudes from an end portion of the hooked portion in the vicinity of a point where the extension of the snare wire intersects toward a base end side of the cylinder.
 3. The endoscopic treatment instrument as recited in claim 1, wherein the locking portion includes a depressed portion or through-hole which is provided on the hooked portion in the vicinity of which the extension of the snare wire intersects.
 4. The endoscopic treatment instrument as recited in claim 1, wherein the locking portion includes a friction generating portion which is provided on an outer surface of the hooked portion and which has a larger coefficient of friction than the outer surface of the hooked portion.
 5. The endoscopic treatment instrument as recited in any one of claims 1, 2 and 3, further comprising a tube which opens at its tip in the cylinder and in which the snare sheath is received so as to be extendable and retractable. 